In a communications system, frame synchronization at a receive end is very important and essential, and data transmission is basically transmission in a frame based format. If the frame synchronization is incorrect, an error of a frame of data is caused. A frame generally includes a preamble signal and data. The frame synchronization is: The receive end determines a start point of data in a frame of a signal by using a preamble signal, and then demodulates the data.
A method for determining a frame synchronization time in the prior art is: A transmit end transmits, in a preamble symbol, a fixed sequence known by a receive end, and the receive end obtains an auto-correlation value M(d) by performing an auto-correlation operation on a received signal, and if the auto-correlation value M(d) exceeds a preset threshold, determines that a current time d is a frame synchronization time, thereby implementing time synchronization. Alternatively, a transmit end transmits, in a preamble symbol, a fixed sequence known by a receive end, and the receive end obtains a cross-correlation value M(d) by performing a cross-correlation operation on a received signal, and if the cross-correlation value M(d) exceeds a preset threshold, determines that a current time d is a frame synchronization time. However, the two existing methods are greatly affected by a carrier frequency offset, which may cause that a correct frame synchronization time cannot be found.